Apparatuses and methods consistent with the present invention relate to detection of a gas. Particularly, the present invention relates to an apparatus and a method for detecting a gas in humid surroundings.
Gas sensors for detecting a fuel gas (hydrogen gas) contained in an exhaust gas of a polymer electrolyte fuel cell are known in the art. For example, a gas sensor disclosed in JP 6-223850 A (see paragraphs 0013 and 0014; FIG. 1) is provided in an exhaust system for discharging a cathode exhaust gas (air) of the fuel cell. This gas sensor is adapted to detect a fuel gas that could accidentally leak from an anode (fuel pole) to a cathode (oxidant pole) through a polymer electrolyte membrane, and used to prevent the fuel gas from being released into the atmosphere.
In general, the exhaust gas of a fuel cell contains a high concentration of water in the form of water vapors or drops derived from water used to humidify the polymer electrolyte membrane or water generated by an electrochemical reaction of the fuel gas (hydrogen gas) and the air (oxygen). On occasion, the water that has condensed from the steam and has thus been contained in the exhaust gas would adhere to a gas sensing element of the gas sensor, which could result in anomalies in performances of the sensing element such as sensitivity for detecting the fuel gas.
With this in view, a gas sensor with a built-in heater has been proposed, for example as disclosed in JP 2003-294675 A (see paragraph 0012; FIG. 4), which can prevent adhesion of the condensed water to the gas sensing element. This gas sensor heats the exhaust gas using the built-in heater to lower the relative humidity.
Typically, when an anomaly occurs in the gas sensor with a built-in heater, the output of the heater is suspended. However, if the heater is suspended without exception when any anomaly appears, including those determined temporarily as an anomaly for example as a result of adhesion of water drops in the exhaust gas to the gas sensing element, such suspension of the heater would cause water condensed more from vapors in the exhaust gas to be further adhered to the gas sensing element. Thus, increase in the amount of water adhered to the gas sensing element would disadvantageously result in prolonged downtime of the gas sensor.
Accordingly, it would be desirable to provide a gas detection apparatus and a gas detection method in which a gas sensor can be swiftly returned to a normal operable state from an abnormal state (with anomalies) caused by adhesion of water to its gas sensing element.
Illustrative, non-limiting embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an illustrative, non-limiting embodiment of the present invention may not overcome any of the problems described above.